The invention relates to a servo valve comprising a valve housing, a valve spindle movable axially within said housing, a drive for operating said spindle, and a position controller for actuating said drive depending on the position of said spindle, and in particular to a servo valve with a drive especially adapted for pneumatic operation.
Servo valves of this kind are disclosed, for example, in Kemmler, U.S. Pat. No. 4,343,224. In this valve design the diaphragm drive is connected by a yoke to the valve housing. The diaphragm drive and the diaphragm are coaxial with the axially displaceable valve spindle which is coupled directly with the diaphragm plate. Beside the yoke is a position controller which by means of a lever detects the stroke of the valve spindle. The bulk, and especially the height, are comparatively great, primarily because of the open fitting of the diaphragm drive to the valve housing and the freely accessible detection of the spindle position by means of the lever of the position control. This open method of construction can lead to difficulties in practice, especially in the application of protective paints to entire apparatus, and accidental losses of adjustment.
Irwin, U.S. Pat. No. 2,895,501 discloses a pressure control with an integrated diaphragm drive, which can be used especially in gas lines for stoves or water heaters. When the valve is open, one chamber of the diaphragm drive is pressurized by the pressure of the medium which flows through the valve, while the other chamber is subjected to pressure in order to open the valve, for example, the pressure of water to be heated. By means of a lever the diaphragm drive shifts the valve body in accordance with the equilibrium of the forces that establishes itself on the diaphragm. Changes in pressure in the chambers corresponding to the momentary pressures of the gas and of the water directly produce a change in the position of the valve body, and it is not easily possible to establish a precise flow cross section through the valve.
A flow controller is also disclosed in Katz et al, U.S. Pat. No. 3,667,722 which has a lever in a sealed chamber which is inserted between an electromagnetic servo drive and a valve. The servo drive contains a pin having a rounded tip which is in contact with one end of the lever. There is no means for detecting the axial position of the valve spindle, nor is there a position controller. Since the pin of the servo drive and also the valve spindle are only touching the lever, additional measures are necessary in order, for example, to maintain contact between the pin and the lever when pin is moving away from the lever.
Finally, a valve operating apparatus is disclosed in Latour, U.S. Pat. No. 2,657,710. The valve body is a component of a piston which is axially displaceable in a cylinder and is biased by a spring. The spring is disposed in a chamber of the cylinder, and this chamber is in communication with a venting valve. The venting valve can be operated by means of an electromagnetic drive and a lever, and the valve movement is limited by means of screws and springs. The position of the valve body integrated into the piston cannot be defined in advance, inasmuch as the valve configured in this manner is either fully open or fully closed, and defined intermediate positions are not easily established.